Known flat springs for revolver-type handguns are used to energize the hammer of a handgun for ignition purposes. These springs generally are substantially flat and are machined and milled or stamped to various geometric shapes in order to provide power output for the hammer. These springs generally provide a linear force function so that the operating force against the trigger is approximately linearly proportional to the hammer position measured in degrees of rotation. The force built up in the spring increases as the hammer is drawn back until the maximum hammer position is reached and the hammer is released. Thus there is a "stack up" period just before the hammer is released during which the force required to squeeze the trigger linearly increases to a level which may cause a shooter to pull off target.
Thus prior springs have left a lot to be desired with respect to a desired smoothness of operation. A smooth trigger pull would allow the shooter to smoothly pull back on the trigger until the hammer is released without a hesitation or "stack up" prior to release of the hammer.
One way that this problem was solved in the past was by using weaker springs. While the weaker springs also built up force linearly, the stacked up force at the end of the hammer travel was less. However the stacked up force at the end of hammer travel was less only because the spring was weaker. The stacked up force of the weaker springs was proportional to the stacked up force of the stronger springs because the force of the weaker springs also increased linearly as a function of hammer rotation. A disadvantage of a spring whose stacked up force was less because it was a weaker spring was a greater risk of misfire because the amount of energy pushing the hammer forward to ignite the cartridge was less.
Milling the cross section of the spring progressively thinner in the direction approaching the claw of the spring is a known method of decreasing stack up. While this method reduced stack up to some degree, it produced a weak point in the spring if the spring was milled enough to significantly reduce stack up because this spring was thinnest in the area where breakage was most likely to occur.
It is also known to taper springs in the direction moving from the butt to the claw providing a non-linear force curve to decrease stackup. Tapering causes the force curve of the spring to be somewhat non-linear allowing more energy to be stored during the early stages of hammer rotation and less stack up closer to hammer release. An example of a handgun having such a spring may be found in the Smith and Wesson Highway Patrolman Revolver Model No. 28.